Insights from BCC Research

Quantum Dots Prove Effective Against Antibiotic-Resistant Superbugs

Among the many types of nanomaterials, quantum dots (QDs) are like no other. At dimensions typically below 10 nanometers (nm), these nanocrystalline semiconductors, metals and magnetic materials are 20,000 times smaller than a human hair and resemble the tiny semiconductors used in consumer electronics.

Today, scientists can precisely synthesize nanocrystalline materials at these critical dimensions (typically < 10 nanometers), and thereby systematically tune their quantum behavior. These tiny particles are making loud noise in terms of enormous interest for exploiting and capitalizing on their unique properties.

For example, researchers at the University of Colorado-Boulder have developed an adaptive, light-activated nanotherapy that may aid in the battle with drug-resistant bacteria. In findings published in the journal NatureMaterials, researchers describe how light-activated QD, or therapeutic nanoparticles, successfully killed 92 percent of drug-resistant bacterial cells in a lab-grown culture.

Antibiotic-resistant bacteria such as Salmonella, E. Coli and Staphylococcus infect some two million people and kill at least 23,000 people in the U.S., according to a news release of the CU-Boulder. Efforts to thwart these so-called “superbugs” have consistently fallen short due to the bacteria’s ability to rapidly adapt and develop immunity to common antibiotics such as penicillin.

“By shrinking these semiconductors down to the nanoscale, we’re able to create highly specific interactions within the cellular environment that only target the infection,” says Prashant Nagpal, an assistant professor in the Department of Chemical and Biological Engineering at CU-Boulder and a senior author of the study.

WHAT IS A QUANTUM DOT?

Quantum dots (QDs) refer to one of several promising materials niche sectors that recently have emerged from the burgeoning growth area of nanotechnology. QDs fall into the category of nanocrystals, which also includes quantum rods and nanowires, explains John Oliver, BCC Research analyst.

As a materials subset, QDs are characterized by particles fabricated to the smallest of dimensions from only a few atoms and upward. At these tiny dimensions, they behave according to the rules of quantum physics, which describe the behavior of atoms and subatomic particles, in contrast to classical physics that describes the behavior of bulk materials, or in other words, objects consisting of many atoms.

More specifically, he says, quantum dots are structures where the electrons within “feel” a three-dimensional (3-D) confinement such that their mobility, based on the exciton Bohr radius, is limited to zero dimensions. In material terms, quantum dots are semiconductor or metallic materials with a size range from a few to a few hundred Angstroms. In essence, a quantum dot can be thought of as an artificial atom.

Previous research has shown that metal nanoparticles—created from gold and silver, among other metals—can be effective at combating antibiotic resistant infections, but can indiscriminately damage surrounding cells as well.

QUANTUM DOTS EMBRACE THE LIGHT IN FIGHT AGAINST INFECTED CELLS

The quantum dots, however, can be tailored to particular infections thanks to their light-activated properties. The dots remain inactive in darkness, but can be activated on command by exposing them to light, allowing researchers to modify the wavelength in order to alter and kill the infected cells.

“While we can always count on these superbugs to adapt and fight the therapy, we can quickly tailor these quantum dots to come up with a new therapy and therefore fight back faster in this evolutionary race,” said Nagpal.

The specificity of this innovation may help reduce or eliminate the potential side effects of other treatment methods, as well as provide a path forward for future development and clinical trials.

“Antibiotics are not just a baseline treatment for bacterial infections, but HIV and cancer as well,” said Anushree Chatterjee, an assistant professor in the Department of Chemical and Biological Engineering at CU-Boulder and a senior author of the study. “Failure to develop effective treatments for drug-resistant strains is not an option, and that’s what this technology moves closer to solving.”

The global market for QDs is estimated to reach $121 million in 2013 and about $3.1 billion in 2018, reflecting a five-year compound annual growth rate (CAGR) of 90.8%. According to Oliver, the biggest growth sectors will be led by optoelectronics (nearly $1.7 billion), solar energy ($640 million) and electronics ($500 million) in the end year.

“Specific QD-enhanced products include biomedical tagants and diagnostics, lasers, optical sensors, flash memory, lighting and displays, solar panels and security deterrents,” Oliver says. “It is projected that in all of these markets, the combined forces of technology push and market pull, due in part to the growing involvement of several multinational partner companies, will lead to a marked increase in both colloidal and in situ QD production.”